Valve assembly for injection molding machine

Abstract

The improved check valve assembly includes a cylindrical barrel, a rotating and reciprocating plasticizing feed screw in said barrel, a screw tip or head portion downstream of the feed screw and connected thereto with the feed screw feeding heated thermoplastic material to the screw tip which in turn feeds the material externally of the screw tip, a check valve assembly between the feed screw and the screw tip including a sliding ring inside the barrel, a first sealing surface of the ring sealable against the feed screw operative to block communication between the feed screw and screw tip, and means operative to seal the ring against the feed screw upon rotation of the feed screw.

What is claimed is: 
     
       1. Injection apparatus comprising a cylindrical barrel; a rotatable and reciprocatable plasticizing feed screw in said barrel; a screw tip downstream of the feed screw and connected thereto and an outlet channel downstream of the screw tip, wherein said feed screw feeds heated thermoplastic material through said outlet channel upon reciprocation of the feed screw; a check valve assembly between said feed screw and screw tip comprising a sliding ring inside said barrel and slidable therein, a first sealing surface of said ring sealable against said feed screw and operative to block communication between the feed screw and screw tip; and means operative to seal the first sealing surface of said ring against said feed screw before reciprocation of the feed screw and upon rotation of the feed screw in one direction. 
     
     
       2. Apparatus according to claim 1 including an outlet channel downstream of said screw tip. 
     
     
       3. Apparatus according to claim 1 including a second surface of said ring sealable against said screw tip to block forward movement of said ring. 
     
     
       4. Apparatus according to claim 3 including at least two balls between said screw tip and ring contacting said screw tip and ring operative to urge said ring into engagement with said feed screw upon rotation of said feed screw in one direction and operative to urge said ring into engagement with said screw tip upon reverse rotation of said feed screw. 
     
     
       5. Injection apparatus, comprising a cylindrical barrel; a rotatable and reciprocatable plasticizing feed screw in said barrel; a screw tip downstream of the feed screw and connected thereto, wherein said feed screw feeds heated thermoplastic material to said screw tip; a check valve assembly between said feed screw and screw tip comprising a sliding ring inside said barrel and slidable therein, a first sealing surface of said ring sealable against said feed screw and operative to block communication between the feed screw and screw tip; means operative to seal said ring against said feed screw upon rotation of the feed screw in one direction; and a profiled cam on said screw tip engagable with a cam surface on said ring operative to urge said ring into engagement with said feed screw upon rotation of said feed screw in one direction and operative to free and said ring for movement into engagement with said screw tip upon reverse rotation of said feed screw. 
     
     
       6. Injection apparatus, comprising a cylindrical barrel; a rotatable and reciprocatable plasticizing feed screw in said barrel; a screw tip downstream of the feed screw and connected thereto, wherein said feed screw feeds heated thermoplastic material to said screw tip; a check valve assembly between said feed screw and screw tip comprising a sliding ring inside said barrel and slidable therein, a first sealing surface of said ring sealable against said feed screw and operative to block communication between the feed screw and screw tip; means operative to seal said ring against said feed screw upon rotation of the feed screw in one direction; and a second surface of said ring sealable against said screw tip to block forward movement of said ring; and at least three balls between said screw tip and ring contacting said screw tip and ring operative to urge said ring into engagement with said feed screw upon rotation of said feed screw in one direction and operative to urge said ring into engagement with said screw tip upon reverse rotation of said feed screw, said balls being circumferentially disposed around said screw tip with each ball running in its own spiral groove. 
     
     
       7. Injection apparatus, comprising a cylindrical barrel; a rotatable and reciprocatable plasticizing feed screw in said barrel; a screw tip downstream of the feed screw and connected thereto, wherein said feed screw feeds heated thermoplastic material to said screw tip; a check valve assembly between said feed screw and screw tip comprising a sliding ring inside said barrel and slidable therein, a first sealing surface of said ring sealable against said feed screw and operative to block communication between the feed screw and screw tip; means operative to seal said ring against said feed screw upon rotation of the feed screw in one direction; and a passageway disposed between said ring and said screw tip communicating with a feed passageway adjacent the first sealing surface of said ring, wherein said ring is slidable against said feed screw to block said communication. 
     
     
       8. Apparatus according to claim 7 including a feed chamber downstream of said passageway and communicating therewith. 
     
     
       9. Injection apparatus, comprising a cylindrical barrel; a rotatable reciprocatable plasticizing feed screw in said barrel; a screw tip downstream of the feed screw and connected thereto, wherein said feed screw feeds heated thermoplastic material to said screw tip; a check valve assembly between said feed screw and screw tip comprising a sliding ring inside said barrel and slidable therein, a first sealing surface of said ring sealable against said feed screw and operative to block communication between the feed screw and screw tip; means operative to seal said ring against said feed screw upon rotation of the feed screw in one direction; and a second surface of said ring sealable against said screw tip to block forward movement of said ring; at least two balls between said screw tip and ring contacting said screw tip and ring operative to urge said ring into engagement with said feed screw upon rotation of said feed screw in one direction and operative to urge said feed screw into engagement with said screw tip upon reverse rotation of said feed screw; and an open groove inside said ring to permit assembly of said screw tip, ring and balls.